Insulin and satiety from feeding in pancreatic-normal and diabetic rats

Insulin's role in food ingestion and satiety was investigated in streptozotocin-diabetic and pancreatic-normal rats. Markedly diabetic rats (60-65 mg/kg b.wt. streptozotocin with mean glycemia of 380 mg/dl) were observed for daily food/water intake and body weight changes and meal pattern in a standard operant chamber. Diabetic animals showed an immediate hypophagia (days 1-4) by decreasing meal size (MS). As animals lost weight, a significant hyperphagia appeared, accomplished by an elevation in MS. Treatment with insulin infused via osmotic minipump at a stable rate (6.0 U/24 h) reduced polyuria and glycemia, eliminated glycosuria, and restored weight gain. MS did not, however, return to baseline immediately. In a second experiment with milder diabetes (20-22 mg/rat streptozotocin, which produced glycemia ranging from 148 to 304 mg/dl), significant hyperphagia appeared, again attributable to an increase in MS. Minipumps infusing 2.4-4.0 U insulin/24 h reversed this hyperphagia. In pancreatic-normal rats, pumps infusing insulin at 1.2 or 2.4 U/24 h produced a modest hypophagia accomplished by a primary decrease in nocturnal intake (11% suppression in dark feeding). Subdiaphragmatically vagotomized rats showed an attenuation of this suppression (no significant effects on food or water intake produced by insulin infused). Insulin appears to participate in satiety by limiting MS, without significantly shortening latency to take the next meal.